commit 10ab825bdef8df510f99c703a5a2d9b13a4e31a5
author Oleg Nesterov <oleg@tv-sign.ru> Wed May 09 02:34:37 2007 -0700
committer Linus Torvalds <torvalds@woody.linux-foundation.org> Wed May 09 12:30:53 2007 -0700
tree e4db81f26c03ba5a5bff43ed44646a4ed4509d67
parent 5de18d169739293e27e0cf9acfc75a2d2f4aa572

change kernel threads to ignore signals instead of blocking them

Currently kernel threads use sigprocmask(SIG_BLOCK) to protect against
signals.  This doesn't prevent the signal delivery, this only blocks
signal_wake_up().  Every "killall -33 kthreadd" means a "struct siginfo"
leak.

Change kthreadd_setup() to set all handlers to SIG_IGN instead of blocking
them (make a new helper ignore_signals() for that).  If the kernel thread
needs some signal, it should use allow_signal() anyway, and in that case it
should not use CLONE_SIGHAND.

Note that we can't change daemonize() (should die!) in the same way,
because it can be used along with CLONE_SIGHAND.  This means that
allow_signal() still should unblock the signal to work correctly with
daemonize()ed threads.

However, disallow_signal() doesn't block the signal any longer but ignores
it.

NOTE: with or without this patch the kernel threads are not protected from
handle_stop_signal(), this seems harmless, but not good.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

diff --git a/kernel/exit.c b/kernel/exit.c
index bc982cd..b0c6f0c 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -347,7 +347,7 @@
 		return -EINVAL;
 
 	spin_lock_irq(&current->sighand->siglock);
-	sigaddset(&current->blocked, sig);
+	current->sighand->action[(sig)-1].sa.sa_handler = SIG_IGN;
 	recalc_sigpending();
 	spin_unlock_irq(&current->sighand->siglock);
 	return 0;